As integrated circuit memory devices such as dynamic random access memory (DRAM) devices have become more highly integrated, the space available for memory cell capacitors has been reduced. Accordingly, there is a need to provide a capacitor on a smaller area while maintaining a predetermined capacitance. In response to this need, materials having relatively high dielectric constants have been used to provide capacitor dielectric layers thereby increasing capacitances. In particular, tantalum pentoxide (Ta.sub.2 O.sub.5) layers have been used, and tantalum pentoxide has good step coverage on complicated lower electrode structures.
When using a material having a high dielectric constant such as tantalum pentoxide to provide a capacitor dielectric layer together with a polysilicon capacitor upper electrode, however, a barrier layer may be needed to reduce reactions between the polysilicon electrode and the tantalum pentoxide dielectric layer. Titanium nitride (TiN) layers formed using physical vapor deposition (PVD) have been used to provide a barrier layer between polysilicon electrodes and tantalum pentoxide dielectric layers. A PVD TiN barrier layer, however, may not provide a sufficiently uniform thickness when used with capacitors having complicated structures such as cylindrical structures, multiple fin structures, or stacked hemispherical grain (HSG) structures. As will be understood by one having skill in the art, a barrier layer generally requires a uniform thickness across even and uneven portions of a dielectric layer. A PVD TiN barrier layer may thus be unsuitable for use with more complicated capacitor structures.
TiN layers formed using chemical vapor deposition have been used to separate silicon substrates and aluminum layers. According to this method, however, the resistance of the TiN layer may be increased due to the chlorine (Cl) in the titanium tetrachloride (TiCl.sub.4) used as the source gas. In particular, this chlorine may remain in the TiN layer after the deposition thereof thereby increasing the resistance of the TiN layer.
A method for removing the Chlorine (Cl) from the TiN layer has been discussed in U.S. Pat. No. 5,279,857, the disclosure of which is hereby incorporated herein in its entirety by reference. As discussed in this patent, a TiN layer is formed using a low pressure chemical vapor deposition (LPCVD) process, and the TiN layer is then annealed in an atmosphere of NH.sub.3 gas. More particularly, the TiN layer is formed on a silicon substrate using TiCl.sub.4, and then the Chlorine in the TiN layer is reduced through a post annealing process in an atmosphere of NH.sub.3 gas, thereby reducing the sheet resistance of the TiN layer.